U.S. patent application number 10/145198 was filed with the patent office on 2002-12-26 for cooling structure for rotating electric machine.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. Invention is credited to Kobayashi, Masakazu, Ohtsuka, Koji.
Application Number | 20020195887 10/145198 |
Document ID | / |
Family ID | 26617310 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020195887 |
Kind Code |
A1 |
Kobayashi, Masakazu ; et
al. |
December 26, 2002 |
Cooling structure for rotating electric machine
Abstract
A cooling structure for a rotating electric machine is proposed
which displays high cooling performance with a simple structure,
does not undergo reductions in efficiency when the rotating
electric machine is operating at high rotation speeds and has high
reliability. The rotating shaft of the rotating element comprises a
hollow structure and an inner cylindrical section which rotates
together with the rotating shaft is provided with a space in an
inner section of the rotating shaft. Coolant flows in an annular
gap between the rotating shaft and the inner cylindrical section.
In this manner, the rotating element is effectively cooled with a
small amount of coolant.
Inventors: |
Kobayashi, Masakazu;
(Yokosuka-shi, JP) ; Ohtsuka, Koji; (Yokohama-shi,
JP) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
NISSAN MOTOR CO., LTD.
|
Family ID: |
26617310 |
Appl. No.: |
10/145198 |
Filed: |
May 15, 2002 |
Current U.S.
Class: |
310/61 |
Current CPC
Class: |
H02K 1/32 20130101; H02K
9/19 20130101 |
Class at
Publication: |
310/61 |
International
Class: |
H02K 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2001 |
JP |
2001-187589 |
Feb 26, 2002 |
JP |
2002-049439 |
Claims
What is claimed is:
1. A cooling structure for a rotating electric machine having a
rotating element which is provided with a rotating shaft having a
hollow structure, the cooling structure comprising: an inner
cylindrical section disposed in the rotating shaft, which rotates
together with the rotating shaft; and an annular gap provided
between the inner peripheral surface of the rotating shaft and the
outer peripheral surface of the inner cylindrical section wherein
coolant flows in the annular gap.
2. The cooling structure for a rotating electric machine as defined
in claim 1, wherein an inner space in the inner cylindrical section
is connected with the annular gap and the coolant remains in the
inner space.
3. The cooling structure for a rotating electric machine as defined
in claim 1, wherein the rotating shaft comprises a first
cylindrical section engaged with a core of the rotating element and
a second cylindrical section disposed on both ends of the first
cylindrical section; and wherein the inner cylindrical section is
disposed in the first cylindrical section; the annular gap and
inner passages of the two second cylindrical sections are
connected; and the coolant flows from one inner passage through the
annular gap to the other inner passage.
4. The cooling structure for a rotating electric machine as defined
in claim 3, wherein the cross-sectional area of the annular gap
perpendicular to a direction of the rotating axis of the rotating
element is smaller than the cross-sectional area of the inner
passages of the second cylindrical section perpendicular to the
direction of the rotating axis of the rotating element.
5. The cooling structure for a rotating electric machine as defined
in claim 3, wherein the inner cylindrical section comprises two
protruding end walls on both ends thereof; each of the inner
passages of the second cylindrical section comprises an enlarging
section respectively facing one protruding end wall; and each
protruding end wall is inserted with a gap into the enlarging
section, the gap being connected with the annular gap.
6. The cooling structure for a rotating electric machine as defined
in claim 1, wherein the width of the annular gap is greater than
0.3 mm.
7. The cooling structure for a rotating electric machine as defined
in claim 3, wherein the inner peripheral surface of the first
cylindrical section comprises a plurality of splines extending in
an axial direction of the first cylindrical section, the plurality
of splines contacting with the outer peripheral surface the inner
cylindrical section to maintain the annular gap.
8. The cooling structure for a rotating electric machine as defined
in claim 7, wherein the splines are divided at one or more
positions in an axial direction of the first cylindrical
section.
9. The cooling structure for a rotating electric machine as defined
in claim 1, wherein the rotating shaft comprises a first
cylindrical section engaged with a core of the rotating element, a
second cylindrical section disposed on one end of the first
cylindrical section and a shaft disposed on the other end, the
inner cylindrical section being positioned in the first cylindrical
section; the annular gap is connected with an inner passage of the
second cylindrical section and the annular gap is connected with
the outside of the rotating element.
10. The cooling structure for a rotating electric machine as
defined in claim 1, wherein the rotating shaft comprises a first
cylindrical section engaged with a core of the rotating element and
one second cylindrical section disposed on one end of the first
cylindrical section; the inner cylindrical section is positioned in
the first cylindrical section; the annular gap and an inner passage
of the second cylindrical section are connected so that coolant
flows from the inner passage into the annular gap.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a cooling structure for a rotating
element of a rotating electric machine.
BACKGROUND OF THE INVENTION
[0002] Tokkai Hei 9-46973 published by the Japanese Patent Office
in 1997 discloses a cooling structure for a rotating element of a
rotating electric machine. The cooling structure as disclosed in
this publication is provided with an injection pipe for cooling
liquid which is fixed to the case. One end of the injection pipe is
inserted into an open end of a hollow rotation shaft of a rotating
element. Cooling liquid is transferred to the center of the
rotating element from the outside.
SUMMARY OF THE INVENTION
[0003] However since cooling liquid in the conventional technique
fills the gap between the hollow rotation shaft which rotates with
the rotating element and the fixed injection pipe, the efficiency
of the rotating electric machine is particularly reduced at high
rotation speeds as a result of the viscosity resistance of the
cooling liquid. Furthermore since the radius of the bearing of the
rotation shaft is large due to the existence of the injection pipe
inserted into the hollow rotation shaft, the bearing loss is
large.
[0004] It is therefore an object of this invention to provide a
simple cooling structure for a rotating electric machine which
displays highly efficient cooling performance and does not result
in reductions in efficiency at high rotation speeds.
[0005] In order to achieve above object, this invention provides a
cooling structure for a rotating electric machine having a rotating
element which is provided with a rotating shaft having a hollow
structure, the cooling structure comprising: an inner cylindrical
section disposed in the rotating shaft and rotating together with
the rotating shaft; and an annular gap provided between the inner
peripheral surface of the rotating shaft and the outer peripheral
surface of the inner cylindrical section. Coolant flows in the
annular gap.
[0006] The details as well as other features and advantages of this
invention are set forth in the remainder of the specification and
are shown in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1A is a sectional view of a rotating element according
to a first embodiment of this invention and FIG. 1B is a sectional
view of an alternative rotating element according to a first
embodiment of this invention.
[0008] FIG. 2 shows a first cylindrical section of a hollow
rotation shaft: FIG. 2A is a front view and FIG. 2B is a sectional
view along the line 2B-2B in FIG. 2A.
[0009] FIG. 3 shows an inner cylindrical section of the hollow
rotation shaft: FIG. 3A is a front view and FIG. 3B is a lateral
view.
[0010] FIG. 4 is an enlarged sectional view of the hollow rotation
shaft in proximity to the inner cylindrical section.
[0011] FIG. 5 shows the first cylindrical section of the hollow
rotation shaft according to another embodiment: FIG. 5A is a front
view and FIG. 5B is a sectional view along the line 5B-5B.
[0012] FIG. 6 is a sectional view of a rotating element according
to another embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Referring to FIG. 1A, a rotating element 1 of a rotating
electric machine is provided with a hollow rotating shaft 2 having
a hollow structure, a plurality of magnetized steel plates 3 which
are provided on an outer periphery of the hollow rotating shaft 2
and are laminated in a direction of the rotational axis of the
rotating element 1, and two endplates 4 fixed to the hollow
rotating shaft 2. The two endplates 4 sandwich the plurality of
laminated magnetized steel plates 3, namely the core of the
rotating element 1. The rotating electric machine is operated for
example as a motor.
[0014] The hollow rotating shaft 2 comprises a first cylindrical
section 5a positioned in a central section of the hollow rotating
shaft 2 and two second cylindrical sections 5b which are stepped
and disposed on both ends of the first cylindrical section 5a. The
first cylindrical section 5a has a constant radius in a direction
of the rotation axis and is inserted and fitted into the plurality
of magnetized steel plate 3. Each second cylindrical section 5b
projects outwardly from each end plate 4, and across the whole
length it has an outer radius and inner radius which are smaller
than the outer radius and inner radius of the first cylindrical
section 5a, respectively. The first cylindrical section 5a is
integrated with the plurality of magnetized steel plates 3 of the
rotating element 1 and the second cylindrical section 5b is fixed
at both ends of the first cylindrical section 5a. A section of the
second cylindrical section 5b is supported to rotate freely on the
casing through a seal and bearing (not shown).
[0015] An inner cylindrical section 6 is inserted into the first
cylindrical section 5a. The inner cylindrical section 6 is
thin-walled and hollow. A narrow annular gap 7 is formed between
the inner peripheral surface of the first cylindrical section 5a
and the outer peripheral surface of the inner cylindrical section
6. The second cylindrical section 5b is fitted to the first
cylindrical section 5a from both sides after assembling the inner
cylindrical section 6 into the inner section of the hollow rotating
shaft 2 of the rotating element 1 so that the inner cylindrical
section 6 is fixed to the rotating element 1. In this manner, the
hollow rotating shaft 2 is provided with the second cylindrical
section 5b on each end.
[0016] The inner section of the second cylindrical section 5b
comprises an inlet passage 15a and an outlet passage 15b. Coolant,
which is introduced from the outside of the hollow rotating shaft 2
to the inlet passage 15a, flows through the annular gap 7 and cools
the inner section of the rotating element 1. Thereafter the coolant
is discharged from the outlet passage 15b to the outside of the
hollow rotating shaft 2.
[0017] When the sectional area of the inlet passage 15a
perpendicular to a direction of the rotating axis is taken to be Ai
and the sectional area of the annular gap 7 perpendicular to a
direction of the rotating axis is taken to be Ac, the following
relationship is established.
Ai.gtoreq.Ac
[0018] Consequently, the flow speed of coolant in the annular gap 7
is increased compared with the flow speed of the coolant in the
inlet and outlet passage 15a, 15b, which increases the cooling
efficiency in turn.
[0019] The inner cylindrical section 6 is divided into two sections
6a, 6b. The sections 6a, 6b of the inner cylindrical section 6 are
open at one end and closed at the other end. The sections 6a, 6b of
each inner cylindrical section 6 are housed in the first
cylindrical section 5a so that the open ends are mutually
opposed.
[0020] The sections 6a, 6b of the inner cylindrical section 6 are
pressed into contact from both closed ends by the two second
cylindrical sections 5b so that the inner cylindrical section 6
rotates together with the rotating element 1. The closed end of the
sections 6a, 6b of the inner cylindrical section 6 comprises a
conical end wall 8, namely a protruding end wall. The conical end
wall 8 is positioned in front of a conical surface 9. The conical
end wall 8 faces a conical surface 9 constituting an enlarging
section of the passages 15a, 15b on an inner section of the second
cylindrical section 5b. The shape of the end wall 8 is not limited
to a conical shape and may be a convex shape which gradually
narrows.
[0021] Referring now to FIG. 2, a plurality of splines 10 are
formed at equal intervals in a peripheral direction on the inner
peripheral surface of the first cylindrical section 5a. The
plurality of splines 10 extends in an axial direction of the first
cylindrical section 5a, in other words in a direction of the
rotation axis. The plurality of splines 10 make contact with the
outer peripheral surface of the inner cylindrical section 6 to
maintain the annular gap 7 and divide the annular gap 7 between the
first cylindrical section 5a and the inner cylindrical section 6
into several equal portions. The splines 10 also have the function
of increasing the cooling efficiency by increasing the surface area
of the inner peripheral surface of the first cylindrical section
5a.
[0022] Referring now to FIG. 3 and FIG. 4, a plurality of tiny
projections 11 are formed on the conical end wall 8 of the inner
cylindrical section 6. The tiny projections 11 have a small size in
comparison with the conical end wall 8. A tiny annular space 14 is
formed between the conical end wall 8 and the conical surface 9
because the tiny projections 11 come into contact with the conical
surface 9 of the second cylindrical section 5b.
[0023] The splines 10 can be manufactured in a cost-effective
manner by an extraction process. The tiny projections 11 can also
be simply manufactured by a pressing process.
[0024] The opposed pair of sections 6a, 6b in the inner cylindrical
section 6 are integrated by being pressed and gripped by the two
second cylindrical sections 5b. However a slit 12 with an extremely
small width is naturally formed along the contact surface of the
sections 6a, 6b of the inner cylindrical section 6 because the
processed contact surface normally comprises tiny undulations. Thus
the width of the slit is so small as not to be apparent to the
naked eye. Since the inner space 13 of the inner cylindrical
section 6 is connected with the outer annular gap 7 because of the
slit 12, a portion of the coolant also fills the inner space
13.
[0025] Referring to FIG. 1B, when the inner cylindrical section 6
is not divided into two sections, the inner cylindrical section 6
can be manufactured as an integrated component. In this case, the
inner space 13 of the inner cylindrical section 6 can be connected
with the outer annular gap 7 by providing a hole 17 in the inner
cylindrical section 6.
[0026] Referring now to FIG. 4, the difference in the inclination
of the conical surface 9 of the second cylindrical section 5b and
the conical end wall 8 of the inner cylindrical section 6 will be
described. Due to the tiny projections 11, the angle .theta.a
subtended by the inner conical face 9 and the rotation axis 30 is
smaller than the angle .theta.i subtended by the conical wall face
8 and the rotation axis 30. The width of the annular space 14
gradually reduces towards the annular gap 7. Consequently, when
coolant flows into the annular space 14 between the conical end
wall 8 and the conical surface 9 from the inlet passage 15a, the
cross-sectional area of the passage of the coolant is gradually
reduced. Thus, the coolant flowing towards the annular gap 7
undergoes rapid acceleration and does not display a large pressure
loss. This result has the effect of reducing pressure loss in the
pump which supplies coolant.
[0027] The above structure allows flow of coolant from the inlet
passage 15a into the annular gap 7 between the inner cylindrical
section 6 and the first cylindrical section 5a. A portion of the
coolant fills the inner space 13 of the inner cylindrical section 6
from the tiny slit 12 which is formed between sections 6a, 6b of
the inner cylindrical section 6 in order to cool the rotating
element 1 from the inside. Thereafter the coolant is discharged
from the outlet passage 15b. Since the coolant has a high flow
speed when flowing through the annular gap 7, the coolant removes
heat from the rotating element 1 in an efficient manner. When a
general-purpose lubricating oil is used as a coolant, it is
preferred that the width d1 of the annular gap 7 is greater than
0.3 mm. This setting improves the cooling efficiency and does not
generate excessive pressure loss. The upper limit of the width d1
of the annular gap 7 are determined from the relationship
Ai.gtoreq.Ac of the cross-sectional area Ai of the inlet passage
15a with the cross sectional area Ac of the annular gap 7.
[0028] The annular gap between the first cylindrical section 5a and
the inner cylindrical section 6 is maintained at equal intervals by
the splines 10. Thus the coolant displays a constant flow rate and
as a result an equal cooling effect is obtained on the entire
periphery of the first cylindrical section 5a.
[0029] The hollow rotating shaft 2 of the rotating element 1 is
formed from a first cylindrical section 5a with a large radius and
a second cylindrical section 5b with a small radius. The
thin-walled inner cylindrical section 6 is disposed in the inner
section of the first cylindrical section 5a. Since a large inner
space 13 is formed in the hollow rotating shaft 2, the weight of
the hollow rotating shaft 2 is low and the inertia of the hollow
rotating shaft 2 is conspicuously low in comparison to a rotating
shaft without an inner space 13. Consequently, the rotating
performance and vibration characteristics of the rotating electric
machine are improved.
[0030] The inner space 13 of the inner cylindrical section 6 is
connected to the annular gap 7 through a slit 12 and coolant also
fills the inner space 13 of the inner cylindrical section 6.
Consequently, even when the temperature or pressure of the coolant
varies, the pressure differential between the inner and outer
sections of the inner cylindrical section 6 is small. As a result,
although the inner cylindrical section 6 which enters the first
cylindrical section 5a is extremely thin, deformation of the inner
cylindrical section 6 is avoided. In other words, it is possible to
prevent the width of the annular gap 7 from being unnecessarily
enlarged and the annular gap 7 from being closed. Consequently
improved stable cooling performance is maintained at all times.
[0031] Furthermore since the bearing on the casing grips the second
cylindrical section 5b with a small radius, bearing loss is reduced
and the rotating element 1 displays excellent rotation
performance.
[0032] Referring to FIG. 5, a second embodiment of this invention
will be described. In the second embodiment, the number of splines
10 is increased in comparison to the first embodiment.
Consequently, the increase in the heat radiating surface makes the
heat radiation effect higher than that in the first embodiment. The
splines 10 are divided at a plurality of positions in an axial
direction by notches 10a. The cooling effect is increased because
the coolant displays turbulent flow at the divided positions.
[0033] Referring to FIG. 6, a third embodiment of this invention
will be described. The hollow rotating shaft 2 is provided with a
first cylindrical section 5a with a large radius, a second
cylindrical section 5b with a small radius disposed upstream side
of coolant flow and a stepped shaft 5c disposed on the downstream
side of coolant flow. The stepped shaft 5c has a small radius in
comparison with the outer radius of the first cylindrical section
5a, over its entire length. The stepped shaft 5c is provided with a
small-radius section 21 and a flange 22. The flange 22 is engaged
with the inner periphery of the first cylindrical section 5a and is
fixed in a position making contact with the inner cylindrical
section 6. The small-radius section 21 is retained on a bearing 20.
A plurality of coolant outlets 23 connected with the annular gap 7
are formed on the flange 22. A baffle plate 24 is disposed in the
passage connecting the inlet passage 15a of the second cylindrical
section 5b with the annular gap 7. This allows the circulation of
coolant to simply follow the rotation of the hollow rotating shaft
2. Furthermore, in this embodiment, the inner space in the inner
cylindrical section 6 is sealed to prevent coolant from
entering.
[0034] In the third embodiment, the coolant flowing in the annular
gap 7 does not undergo a large resistance because it is discharged
to the outside of the rotating element 1 from a coolant outlet 23.
As a result, it is possible to reduce the pressure loss in the
coolant in comparison to the first embodiment in which coolant
flowing through the annular gap 7 is recirculated to the outlet
passage. In addition, the discharged coolant can be used in order
to lubricate the bearing 20.
[0035] The entire contents of Japanese Patent Applications
P2001-187589 (filed Jun. 21, 2001) and P2002-49439 (filed Feb. 26,
2002) are incorporated herein by reference.
[0036] Although the invention has been described above by reference
to certain embodiments of the invention, the invention is not
limited to the embodiments described above. Modifications and
variations of the embodiments described above will occur to those
skilled in the art, in light of the above teachings. The scope of
the invention is defined with reference to the following
claims.
* * * * *